This invention relates generally to an offset axle assembly and specifically to an offset axle assembly that allows greater distance between axles.
Typically, an offset axle is used to provide an offset distance between a drive axle and the wheel centerline. In some applications, the drive axle is positioned above the wheel centerline to provide increased ground clearance. In other applications, the drive axle is positioned below the wheel centerline to provide for a lower floor. The lower floor is typically used in public transportation vehicles such as large buses. By placing the drive shaft significantly lower than the wheel centerline the floor of the bus can be significantly lowered to improve ingress and egress from the vehicle.
Offset axles are typically configured to include a drive gear and a driven gear. The driven gear drives an axle, which in turn drives the wheels. The drive gear assembly typically includes a drive gear driven by a shaft through a differential assembly. The drive gear drives a pair of idler gears that in turn drive the driven gear. The idler gears provide direction reversal and speed reduction.
A conventional offset axle assembly is shown in prior art FIG. 1. The prior art offset axle 10 includes a gear case housing 12 that supports the drive gear 14 that drives the driven gear 15 and shaft 16. The shaft 16 is suspended between the driven gear 15 and a hub 26. Bearing assemblies 34 supports the driven gear 15. Additional bearing assemblies 34 support the hub 26. In this configuration, the shaft 16 extends through a spindle 20 bolted to the gear case 12. The shaft 16 attaches on one end to the driven gear 15 and to another end to the hub 26. The hub 26 is in turn supported for rotation about the spindle 20 by the bearing assemblies 34. Attached to the hub 26 is the drum 24. The drum 24 cooperates with the brake shoes 30 to provide braking force. To support the brake shoes 30 a separate brake support 22 is mounted to the gear case 12 separate of the spindle 20. The brake support 22 includes a brake support lug 28 supporting the brake shoes 30.
In operation, power transmitted through the differential assembly 32 drives the drive gear 14 which drives the driven gear 15 rotating the shaft 16 and hub 26. For any maintenance to be accomplished on the brake assembly such as changing shoes 30, the hub must be removed to service the brakes 30. Removal of the hub 26 requires that a total of 68 screws be removed in order to service both wheel ends of the offset axle 10. This is very labor intensive and discourages frequent maintenance of the brake shoes 30. Further, the offset axle assembly shown at 10 includes additional bearing assemblies 34 to support the hub 26 along with the gear 15. As appreciated, reducing the number of bearing assemblies is desirable to reduce maintenance and decrease manufacturing costs.
Accordingly, it is desired to develop a simplified offset axle assembly that reduces the number of bearing assemblies and eases routine maintenance and increases feasible offset distances between axles.
An embodiment of this invention is a two-piece gear case housing supporting a driven gear, shaft, hub and including an integral brake support structure to simplify construction and maintenance.
An embodiment of this invention includes a gear case housing comprised of two pieces. The first piece encloses a differential assembly along with the drive gear assembly. The second portion of the gear case includes a cavity with two bearing assemblies to support rotation of the driven shaft along with the driven gear and hub. The driven gear is attached to the driven shaft and rotationally supported within a cavity of the second half of the gear case. The shaft includes a spline onto which a hub is installed. The hub is secured to the shaft by a single nut engaging threads on the shaft.
An outer portion of the second gear case housing includes a brake shoe support lug. The brake shoe support lug eliminates the need for a separate brake support structure currently part of conventional offset axle configurations. The two-part gear case eases maintenance of the brake system by simplifying removal of the hub with a single nut securing the hub to the shaft.
The offset axle of this invention includes two bearing assemblies disposed within the cavity defined by the second half of the gear case. The two bearing assemblies support the driven gear, the driven axle along with the hub. This reduces the number of bearing assemblies from four in conventionally configured offset axle assemblies to two. As appreciated, reduction of bearing assemblies required to support rotating components decreases cost of the overall axle assembly and improves durability and operation.
Another embodiment of this invention includes a drive gear assembly comprising a planetary gear system. The planetary gear system includes a ring gear having gear teeth positioned on an inner circumference and an outer circumference. The driven gear is positioned at a center point within the ring gear to drive a plurality of planetary gears. The planetary gears in turn rotate the ring gear, which in turn drives the driven gear. This configuration provides for an increase in the distance between the drive axle and the driven axle.
Still another embodiment of this invention is a driven gear assembly comprising a planetary gear system driven by a helical drive gear. A helical driven gear is suspended for rotation by a pair of bearing assemblies disposed at each end of a helical gear. The helical gear includes a driven portion engaged with the drive gear and a shaft portion engaged with planetary gears disposed within a ring gear. The ring gear of this assembly is integral to the shaft. In operation, the helical drive gear drives the helical driven gear portion, which in turn rotates the shaft portion of the helical gear, engaged through the planetary gears of the planetary gear system. The planetary gear system in turn engages gear teeth disposed on an inner surface of the ring gear integral to the shaft. This configuration allows for increased offset distances between the drive axle and the driven axle to improve ground clearance or further lower the floor of a transportation vehicle.
Accordingly, embodiments of this invention provide an improved and more efficient offset drive axle assembly allowing greater offset distances between axles while easing maintenance.